Visual display systems are commonly used to simulate training environments where training through actual operations would be dangerous, expensive or otherwise impractical. One common application for visual display systems is flight simulation and training systems. A typical flight simulation and training system requires visual "out the window" images simulating the terrain, landscape, cultural features, buildings, vehicles, and other aircraft in the simulated vicinity of the trainee. One form of conventional flight simulator includes the projection of images onto the inside of a large spherically-shaped dome or partial dome structure. The images are displayed inside the domes using multiple video projectors and associated optical devices mounted inside the domes. These projectors and optics must be carefully positioned inside the domes in order to properly display the simulated images. Another conventional form of a flight simulator typically includes one or more video display screens onto which video images are projected by one or more projectors, such as cathode ray tubes. The video images may be projected onto the display screens from either the front or the rear of the screens. An example of such a conventional flight simulator is the Virtual Image Display Simulator (VIDS), manufactured by The Boeing Company, the assignee of the current invention. The VIDS provides four rear-projected video screens positioned a few feet from the trainee used to display simulated images in front of the trainee and up to three additional rear-projected display screens used to display simulated images behind the trainee. Conventional flight simulators also usually include a control panel and a control stick and throttle for providing input to the visual display system in response to the displayed video images. The control panel and surrounding pilot environment are often realistic simulations of the controls and displays present in the actual aircraft. Thus, the operator can simulate the flight of an aircraft and can respond to the environment as depicted by the visual display.
One primary objective of flight simulators is to enhance and optimize the simulated images to present the operator with a high fidelity and realistic training environment. Problems experienced by conventional flight simulators include diminished brightness and contrast, and a low resolution of the projected images. These problems arise in large part because of the capability of conventional video projectors, and the use of a relatively small number of video screens (necessitating that each video projector project a relatively large image). Additionally, conventional flight simulators generally provide a simulated image that is focused relatively close to the trainee's eyes, and not at a far distance. An improved flight simulator would produce a virtual image that is focused at or near infinity so that the virtual image appears sufficiently real to the simulation pilot. Such an improved flight simulator would be of great assistance to one particular simulation scenario, namely air-to-ground training, which requires eye-limited resolution, i.e., display resolution that meets or exceeds the resolution of the human eye. Another drawback to conventional flight simulators is the size of the projectors, display screens, and associated electronics and optics. An improved flight simulator would have a reduced overall size, allowing the entire simulator to be located in a small room, thus reducing the cost of installing and operating the flight simulator.
For the foregoing reasons, there is a strong need for an improved visual system for use, for example, as a flight simulator. Preferably, the system would have enhanced brightness, contrast and resolution over existing visual systems and produce a virtual image focused at or near infinity. A preferred visual system would be of relatively compact size and designed using upgradeable, commercially-available components.